They found that foods that created a healthy response in some participants produced an unhealthy blood sugar spike in other participants.

ABC

Drs. Eran Segal and Eran Elinav are the authors of a new book, "The Personalized Diet."

The key to weight loss, according to Segal and Elinav, is watching how your blood sugar reacts to different foods.

“For years, we've been trying to search for that silver-bullet diet that would work for everybody and we've been miserably failing,” Segal told ABC News. “And that's because the best diet for each person really has to be tailored to that individual.”

There is not yet any "evidence-based science" to support the practice of blood sugar monitoring for weight loss, according to ABC News' chief medical correspondent Dr. Jennifer Ashton, who also holds an M.S. in nutrition.

"I completely agree with the fact there is no one size fits all for a diet. You have to find what works for you," Ashton said today on "Good Morning America." "But at this time there is no rigorous, peer-reviewed, evidence-based science to support the practice of checking your blood sugar after you eat."

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A woman uses a blood glucose measurement to check her blood.

Ashton also stressed that the concept of using blood sugar levels to create an individualized approach to a diet applies to non-diabetics only.

The program laid out in Segal’s and Elinav’s book, “The Personalized Diet,” focuses on finding which carbohydrates are best for each person. Determining that, they say, requires testing your blood sugar via a finger prick after meals.

“Our solution gives you a way to find out which carbohydrates would actually be best for you to integrate into what we believe would be a healthy diet for you,” Segal said.

Segal and Elinav say their algorithm, based on blood sugar reactions, determines what foods you should avoid and what foods to add to your diet.

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A woman checks here weight on a bathroom scale in this undated stock photo.

Some people, for instance, may be able to eat white bread, instead of wheat, while others may need to spread fats like avocado, olive oil or butter on the bread.

“What we were surprised to find out was just like any other food, there is no such thing as a good bread,” Elinav said. “The response to bread was completely individualized.”

Other foods sometimes not associated with diets, like cheese, are fine to eat for weight loss, as long as they are not paired with a carbohydrate, according to the pair’s research.

ABC

Drs. Eran Segal and Eran Elinav, of Israel's Weizmann Institute of Science, tested blood sugar levels in 1,000 people after every meal.

“When you don't have carbohydrates, those foods will not spike your blood sugar levels,” Segal said.

Segal and Elinav also found that traditional pre-competition foods for athletes like bananas and dates, both high in carbohydrates, may actually cause more fatigue.

When it comes to achieving weight loss, Ashton recommends taking an approach that is "safe, simple and sustainable."

She also added a fourth item to the list, saying, "You have to watch the sugar."